This invention relates to fluid displacement apparatus and, more particularly, to an improved axial sealing device for a scroll-type fluid compressor.
Scroll-type apparatus are well-known in the prior art. For example, U.S. Pat. No. 801,182 discloses the basic construction of a scroll-type fluid displacement apparatus that includes two scroll members, each having a circular end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that the spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces, which define and seal off at least one pair of fluid pockets. The fluid pockets are defined by the line contacts between the interfitting two spiral elements and the axial contacts between the axial end surface of one spiral element and the inner end surface of the end plate supporting the other spiral element. The relative orbital motion of the two scroll members shifts the line contacts along the spiral curved surface, thus changing the volume of the fluid pockets. Since the volume of the fluid pockets increases or decreases dependent on the direction of the orbital motion, the scroll-type fluid displacement apparatus is applicable to compress, expand, or pump fluids.
In comparison with conventional compressors of the piston type, the scroll-type compressor has certain advantages, such as fewer parts and continuous compression of fluid. However, one of the problems with scroll-type compressors is the ineffective sealing of the fluid pockets. Axial and radial sealing of the fluid pockets must be maintained in a scroll-type compressor in order to achieve efficient operation.
Various techniques have been used in the prior art to resolve the sealing problems, in particular, the axial sealing problem. In U.S. Pat. No. 3,334,634, a seal element is mounted on the axial end surface of each spiral element. The end surface of each spiral element facing the end plate of the other scroll member is provided with a groove along the spiral. The seal element is placed within each of the grooves together with an axial force-urging means, such as a spring. The axial force-urging means urges the seal element toward the facing end surface of the end plate to thereby effect the axial sealing.
Because the seal element in the above-cited patent is urged toward the facing end surface of the end plate by a spring or other axial force-urging mechanism, over a period of time abrasions occur between the end surface of the seal element and the end plate of the scroll member, especially when lightweight alloys such as aluminum alloys are used for the material of the scroll member. These abrasions result in undesirable wear and create tiny abrasion particles or dust. The wear creates damage to the parts of the apparatus (e.g., to the surface of the scroll members). When the scroll device is used as the compressor in an air-conditioning system, for example, the abrasion particles adversely affect the operation of the filter and expansion valve for the refrigerant circuit. As the end plate wears because of abrasion, the seal elements are also damaged, and the axial contact between the end surface of spiral element and the inner end surface of the end plate becomes imperfect, which dimishes compressor efficiency.
To avoid these disadvantages, an improved axial sealing device is described in commonly assigned co-pending application Ser. No. 312,755 filed on Oct. 19, 1981. In this application, an involute anti-wear plate is disposed between the axial end surface of the seal element and the circular end plate of one or both scrolls. However, one of the scrolls, preferably the fixed scroll, must have a discharge port at or near the center of the spiral element and end plate. Therefore, if an anti-wear plate is disposed on the scroll which has the discharge port, the center portion of the anti-wear plate constructed as disclosed in the above-cited co-pending application covers or partly covers the discharge port. It has been found that during the operation of a scroll device so constructed, the fluid passing through the discharge port strikes against the center of the anti-wear plate and causes undesirable vibration of the plate which may result in breakage or damage to the central portion of the plate.